different assigned materials into one texture?
When you UV unwrap and create a new image, save the black image as whatever you want your final map to be called. Then add an image texture to any of those materials (it doesn't matter which one) and open up the file you just saved. You don't have to plug it up to anything, just make sure it's selected. Now make sure your object is selected, then tell it to bake. If you only want the colors and want to add your lighting another way, make sure you only have 'color' selected in your options. When it bakes, it should appear on image texture, but make sure to save it (you can do this in the UV image editor).

Now you can delete all your materials and use your mapped colors as the color input for any node that accepts a color input!